The present invention relates to an ion implanting apparatus for fabricating a highly-integrated device by ion-implanting boron, phosphorous, arsenic or the like into a silicon semiconductor, or fabricating a silicon substrate having an embedded insulator layer by ion-implanting and oxygen, nitrogen, and more particularly relates to an ion implanting apparatus suitable for large current ion-implanting in which ions are implanted into a silicon wafer having a small ratio of surface area covered with an insulator, while the silicon wafer is being maintained at a high temperature.
FIG. 2A and FIG. 2B show a conventional ion implanting apparatus. FIG. 2A is the front view and FIG. 2B shows the construction of the ion implanting chamber seeing from the side of a beam 4. In the figure, the other main constituting parts such as an ion source, a mass separator, a lens, a slit, a deflector and so on are not shown. There are a lot of conventional ion planting apparatuses of such types, and one of them is disclosed, for example, in U.S. Pat. No. 5,089,710.
As shown in the figure, a surface of a silicon wafer 2 to be implanted with ions is generally patterned with an insulator film such as an SiO.sub.2 film or a resist, and accordingly the area of exposed silicon base is small.
A plurality of wafers 2 are mounted on a surface of a rotating disk 1 having a diameter of, generally, one meter or so. In order to perform uniform implanting, the rotating disk 1 is mechanically moved to and fro in the radial direction shown by a line having both side arrows in FIG. 2B.
Since an insulator film covers a large portion of the surface of a silicon wafer 2 in the prior art, the insulator film is charged by irradiation of an ion beam 4. The ion beam 4 is expanded by the charged insulator film and consequently uniform implanting cannot be performed due to change in the current density of the ion beam during ion implanting. Further, an electric breakdown is produced in the insulator film to break the element itself formed on the silicon wafer 2.
In order to solve such a problem, in the past, electrons are supplied together with the ion beam 4. As the electron supply methods in the prior art, there is a method in which an electron beam generating unit is arranged in the middle of the ion beam 4 near the wafer, as shown in FIG. 2A. The ion beam generating unit is generally composed of a heated filament 6 and an electrode extracting electrons from the filament 6 to generate a primary electron beam 7. The electron beam 7 is irradiated on a secondary electron emitting plate 5 to generate a lot of secondary electrons from the secondary electron emitting plate 5 and the secondary electrons are supplied to the silicon wafer 2. The reason why the electron beam 7 is not directly irradiated onto the silicon wafer 2 is that a large quantity of impurity elements are generally released from the heated filament 6 when the heated filament 6 is heated and contamination of the wafer by even a very small quantity of impurity elements is not allowed in fabrication of a highly integrated device.
Referring to FIG. 2A, it is well known that an electron beam 7 having an energy higher than 100 eV is usually not efficiently taken in the ion beam 4. In order to take in the electron beam efficiently, it is necessary that the energy of the electrons is reduced to a value smaller than several tens eV.
Because of the above reason, in the prior art, a large quantity of secondary electrons are generated and irradiated onto the silicon wafer 2 though an electron generating unit that has a complex construction and requires an electric power source and so on.
The prior art is characterized by the ion beam 4 being implanted inside the silicon wafer 2 through an insulator film covering the silicon wafer 2 and it is required to pour electrons onto a surface of the silicon wafer being irradiated with the ion beam in order to prevent the wafer from being charged.
However, in the industrial field of semiconductor ion implanting in recent years, a method of using ion implanting is growing wider. In the method, a silicon substrate which has no insulator film on its surface but has an insulator film formed within is fabricated by implanting an element forming an insulator by chemically reacting with silicon.
The ions used are oxygen ions, nitrogen ions and so on. The ion implanting is performed while the semiconductor wafer is being kept at a high temperature from several hundreds .degree. C. to near 1000.degree. C. In this ion implantation, since there is no insulator film on the surface of the semiconductor wafer, the heated filament 6 and the electron generating unit including the secondary electron emitting plate 5 shown in FIG. 2 are not required.